1. Field of the Invention
The present invention relates to a semiconductor optical device including a spot-size converter.
2. Description of the Related Art
Japanese Unexamined Patent Application Publication No. 5-142435 (Patent Literature 1) discloses a waveguide-type beam conversion device for spot-size conversion. Japanese Unexamined Patent Application Publication No. 9-15435 (Patent Literature 2) discloses an optical coupling device for spot-size conversion.
The beam conversion device disclosed in Patent Literature 1 includes an upper cladding layer and a lower cladding layer that sandwich a main core layer, in which each of the cladding layers includes a plurality of auxiliary core layers and a plurality of cladding layers that are alternately arranged. In the upper cladding layer and the lower cladding layer, the auxiliary core layers function so as to enhance the electric field amplitude of light, and the shape of the electric field profile of the beam conversion device has a plurality of peaks. In the beam conversion device, a spot size on a facet of the device is expanded due to the electric field profile having the plurality of peaks, thereby reducing coupling loss between the beam conversion device and the external optical waveguide.
The optical coupling device disclosed in Patent Literature 2 includes a cladding region having a projecting portion that is located right on a core layer. This projecting portion functions so as to increase the thickness of a cladding region right on the core layer. The increased thickness of the cladding region can make a spot size of the optical coupling device expanded, thereby reducing coupling loss between the optical coupling device and the external optical waveguide.